The invention relates to overrunning coupling assemblies having relatively movable coupling plates with juxtaposed planar surfaces.
It is known design practice in the management of torque in a power transmission mechanism to use overrunning couplings in combination with friction elements, such as friction brakes or friction clutches, as torque transfer paths are established and disestablished between a driving member and a driven member. An example of an overrunning coupling in an environment of this type may be seen by referring to U.S. Pat. No. 5,413,539 (referred to as the ""539 patent), which discloses a multiple-ratio, geared, automatic transmission for automotive vehicle powertrains. The overrunning coupling disclosed in the ""539 patent is a conventional roller clutch assembly that serves as a reaction torque transfer element when the gearing for the transmission is conditioned for intermediate speed ratio operation. It distributes reaction torque to the transmission casing when a forward-drive friction clutch is engaged.
It is known design practice also to substitute an overrunning planar clutch assembly for the roller clutch assembly of the design of the ""539 patent so that the overall axial dimensions of the transmission gearing can be reduced to a minimum and the assembly procedure can be simplified. An overrunning planar clutch assembly of this kind is disclosed, for example, in U.S. Pat. No. 5,918,715, and U.S. Pat. No. 5,979,627 (referred to as the ""715 patent and the ""627 patent, respectively), both of which are assigned to the assignee of the present invention.
The planar clutch assemblies of the designs shown in the ""715 and ""627 patents include a pocket plate and a notch plate disposed in juxtaposed relationship, one with respect to the other, about a common rotary axis. Angularly spaced pockets or recesses are formed in a planar surface of a first plate, and notches are formed at angularly spaced locations in the planar surface of a companion second plate. Torque-transmitting struts are located in the pockets of the first plate so that they may pivot about an anchor point in each pocket. A spring is mounted in each pocket for the purpose of biasing the associated strut for pivotal movement about the anchor point so that one edge of the strut will engage a recess or notch formed in the planar surface of the second plate. This locks the plates together when relative torque transfer through the coupling assembly is in one direction while allowing freewheeling motion of one plate relative to the other when torque transfer is reversed.
It is an objective of the invention to provide a simplified, inertiaactuated overrunning coupling with planar coupling plates and with torque transmitting struts situated between the plates for torque transfer from one plate to the other in one direction but which will permit freewheeling motion of one plate relative to the other when torque is reversed. It is an objective also to eliminate the need for springs to urge the individual struts of the coupling assembly into engagement with the notch plate, thereby simplifying the overall assembly and simplifying the assembly process during manufacture of the coupling assembly.
An inertia ball is mounted in each pocket of the pocket plate. The pocket is formed with a ramp that is engaged by the inertia ball so that an inertia force component acts on the companion strut to urge the strut into engagement with the recesses or notches of the notch plate.
The inertia force component applied by the inertia ball on each of the struts eliminates the need for assembling individual springs for the struts, as in the case of the design of the ""627 and ""715 patents.
The improved coupling assembly of the invention eliminates ratcheting noise that typically is characteristic of a planar clutch in which the individual struts are spring-biased into engagement with a notch plate. It eliminates also a substantial degree of wear of the strut surfaces when the coupling is in an overrunning mode.
The cooperating parts of the clutch assembly may be made with alternate materials, unlike prior art designs where the mating parts typically are formed using powdered metal process steps. The use of alternate materials makes it possible to use alternative heat treatments for the struts because wear normally associated with ratcheting of the struts against the notch plate is not a design issue.
The pocket design of the pocket plate of the present invention allows the struts to rest on flat surfaces on the pocket plate during the overrunning mode. When the struts are activated by the inertia balls to a torque transfer mode, one edge of the struts will tip into a recess formed in the associated pockets whereby the opposite edges of the struts move to a position where they engage the recesses of the notch plate.
The inertia balls of the improved coupling assembly of the invention actuate the struts with a force that is determined by the rate of deceleration of the pocket plate. In the structural environment of an automatic transmission gearset, the pocket plate decelerates rapidly during a shift sequence. This rapid deceleration applies a constant force on the strut to effect engagement of the coupling assembly as the pocket plate angular velocity approaches zero and begins to reverse direction. Initial engagement of each strut with the notch plate face then will allow a margin of the struts to cam or wedge into full engagement with the notches of the notch plate, thereby achieving full reaction torque transmitting capacity at the instant a shift sequence in the transmission is commanded by the transmission control system.
In practicing the invention, a pocket plate and a notch plate are assembled in a torque flow path from a torque input member to a torque output member. The pocket plate and the notch plate have annular planar surfaces that are arranged on a common rotary axis in juxtaposed, close proximity, one with respect to the other. Angularly spaced pockets in the pocket plate and angularly spaced notches in the notch plate are located so that they are equidistant from a common geometric axis.
A primary ramped surface is formed in each pocket. A torque transmitting strut in each pocket has an anchor edge engaging the pocket plate and a movable edge engageable with the notch plate during operation of the coupling assembly in a locked mode.
Inertia members, or balls, are located in the pockets. These engage the ramped surfaces in the pockets so that inertia forces acting on the balls urge the struts into engagement with the notches in response to deceleration of the pocket plate.
Another feature of the invention comprises secondary ramped surfaces in the pockets, which are engaged by the balls as centrifugal forces on the balls are developed. The centrifugal forces develop a strut engaging centrifugal force component to initiate an instantaneous coupling assembly response to deceleration forces acting on the balls in the pocket plate. The faster the pocket plate rotates, the greater the ball force component becomes for any given secondary ramped surface angle.
The present invention is an overrunning coupling assembly comprising a pocket plate and a notch plate. One plate is connected to a torque input member and the other plate is connected to a torque output member. The pocket plate has a pocket plate planar surface and the notch plate has a notch plate planar surface. The planar surfaces are assembled on a common axis in juxtaposed close proximity. A plurality of angularly-spaced pockets are in the pocket plate planar surface, and a plurality of angularly-spaced notches are in the notch plate planar surface. A ramp surface portion is in each pocket. A torque-transmitting strut is in each pocket, each strut having an anchor edge engageable with the pocket plate and a movable edge engageable with the notch of the notch plate during operation of the overrunning coupling assembly in a locked mode. Inertia members are in the pockets between the struts and the ramp surface portion whereby inertia forces acting on the inertia members urge the struts into engagement with the notches in response to rotary inertia forces acting on the inertia members.